I've been thinking lately about giving Tirelat more of a history, trying to figure out how it got the way it is (and potentially connecting it with other related languages if you go back far enough). One of the issues is what happened to the /ð/ phoneme which existed at least in some dialects. In some cases it merged with /d/ and in others with /v/. I figure something like a conditioned merger must have happened. But I've been trying to understand what happened in General American with the phoneme that ended up as /ɒ/ in RP, and I can't find any consistent features that would explain the splits and mergers. Is it possible that phoneme mergers and splits between dialects of a language can be irregular, with some words going one way and some words another, in a more or less arbitrary way? It looks like most words with /ɒ/ in RP have either /ɑ/ or /ɔ/ in General American. In cases where GenAm has /ɔ/, the following consonant is often -f -g, -ŋ, -r, -s, or -θ. If the following consonant is -l, it can go either way (doll, follow, solid, tolerant with /ɑ/ vs. dolphin, golf, malt, solve with /ɔ/). But maybe it depends on whether the /l/ is followed by another consonant. So if this is a conditioned merger, it's a pretty odd set of conditions. But even this set of rules seems to be incomplete, since there are apparent exceptions. You'd expect "hostage" and "hostile" to have /ɔ/ (like "cost" or "lost"), but they have /ɑ/. Other apparent exceptions that have /ɑ/ where you might expect /ɔ/ include "borrow", "cog", "jostle", and "wasp". There's also "sorry", which the way I say it is anomalous in having /ɒr/ where no other words have /ɒ/ before /r/. And before -ʃ, it looks like /ɒ/ can go either way (Josh with /ɑ/ vs. wash with /ɔ/), but there are too few examples to generalize. Might there have been some regularity in the splits and mergers that was obscured by later sound changes? Or is it possible that phonemes with only marginal contrast can be lost in unpredictable patterns? (I can only think of "coral" vs. "choral" as a contrast that was lost in the mergers, but there may be a few others.) I'm thinking that Tirelat /ð/ may have been an uncommon phoneme in the first place, so I can probably come up with a set of conditions that determine whether it merges with /v/ or /d/ without being too inconsistent with the existing vocabulary. But it would be nice to make sense of how these kinds of change can happen in general.